Closing, locking and prestressing device for casting molds

ABSTRACT

The device is usable for casting molds, particularly for injection and pressure molding, of the type having a fixed mold part carrier, a supporting part having a shifting device attached thereto, at least two guides extending from the fixed carrier to the supporting part, a mold part carrier movable by the shifting device along the guides and anchorable thereon, and a hydraulic prestressing device acting through the guides upon the two mold part carriers. Two guide bars extend parallel to the shifting device through the supporting part in guided relation therein, and are connected to the movable mold part carrier. At least one stop plate is movable on the shifting device and is connected to the two guide bars, and two mechanical stops provided on opposite sides of the stop plate are cooperable therewith. Each guide bar is provided, between the supporting part and the movable mold part carrier, with a piston and also supports a movable cylinder enclosing the piston. Each cylinder is connected to an ejector plate, and cavities on opposite sides of the piston, inside the associated cylinder, are controllably chareable hydraulically. The guides, adjacent that surface of the fixed mold part carrier away from the casing mold, provided prestressing pistons each movable in a cylinder on the fixed mold part carrier.

United States Patent [I 1 Eggenberger et al.

1 1 CLOSING, LOCKING AND PRESTRESSING DEVICE FOR CASTING MOLDS [76]Inventors: Ulrich Eggenberger, Bichwilerstrasse, Oberuzwil; Heinz Nef,Dammweg, Uzwil, both of Switzerland [22] Filed: Mar. 22,1971

[21] App]. N0.: 126,567

[ 56] References Cited UNITED STATES PATENTS 2,862,238 12/1958 Cuzzi..425/450 3,263,277 8/1966 Ohlendorf et al. ..425/450 3,289,252 12/1966Bromleg ..425/45() X 3,351,982 11/1967 Jackson et al. ..425/45()3,359,598 12/1967 Bucy ..425/45(l X 3,372,433 3/1968 Nouel ..425/45()3,590,437 7/1971 Annis, Jr. et a1 ..425/450 X Primary Examiner-Robert L.Spicer, Jr. Attorney-John J. McGlew and Alfred E. Page 1 Apr. 24, 1973[5 7] ABSTRACT The device is usable for casting molds, particularly forinjection and pressure molding, of the type having a fixed mold partcarrier, at supporting part having a shifting device attached thereto,at least two guides extending from the fixed carrier to the supportingpart, a mold part carrier movable by the shifting device along theguides and anchorable thereon, and a hydraulic prestressing deviceacting through the guides upon the two mold part carriers. Two guidebars extend parallel to the shifting device through the supporting partin guided relation therein, and are connected to the movable mold partcarrier. At least one stop plate is movable on the shifting device andis connected to the two guide bars, and two mechanical stops provided onopposite sides of the stop plate are cooperable therewith. Each guidebar is provided, between the supporting part and the movable mold partcarrier, with a piston and also supports a movable cylinder enclosingthe piston. Each cylinder is connected to an ejector plate, and cavitieson opposite sides of the piston, inside the associated cylinder, arecontrollably chareable hydraulically. The guides, ad-

jacent that surface of the fixed mold part carrier away from the casingmold, provided prestressing pistons each movable in a cylinder on thefixed mold part carricr.

9 Claims, 2 Drawing Figures Patented April 24, 1973 2 Sheets-Sheet lPatented April 24, 1973 2 Sheets-Sheet 2 CLOSING, LOCKING ANDPRESTRESSING DEVICE FOR CASTING MOLDS BACKGROUND OF THE INVENTION At arelatively early stage in the development and introduction of metalpressure casting and plastic injection molding, for the production ofparts of any shape in spatially defined, mold-like casting guides,permitting the production of thousands of identical parts, thedifficulty of using presses such as used previously for casting moldingwas recognized. This difficulty is that, with increasing size of theparts to be manufactured by pressure or injection molding longer andlonger strokes of the mounting parts accompanying the mold halves arerequired. Consequently, the guide bars extending between the fixed moldpart carrier and a supporting part, and which support the shifting andprestressing device, and along which guide bars the movable mold carriermoves, become longer and longer. This leads to greater and greaterelongations of these guide bars during the prestressing period andduring the casting operation.

Consequently, ways were sought to greatlyreduce this elongation, forexample, to have the actual mold tension and its reactive force intension members become active, by suitable measures, between a fixed andmovable mold part carrier only. Thus, suggestions have been made, wheremold carries movable relatively to each other were involved, to bringinto mutual, force-closing engagement between the fixed and movable moldpart carrier, several, and in certain cases a large number of, shorttension rods by a suitable mechanical means, and then to build up onlythrough the short tension rods the great mold prestressing forces byusing multi-part mold part carriers presenting the locking elements onthe one hand and mold mounting plates shiftable relative to the formeron the other hand.

Similar suggestions have again been made very recently, all aimed atmaking the balance of forces economical in such machines by reducing themaximum possible elongations of tension rods. The suggestions made sofar have disadvantages which must be overcome. In the devices alreadyproposed, the masses to be moved are very great, in that the locking andprestressing elements are disposed in the movable mg ld carrier.

The disadvantage of another device, which is also known, is that thetension rods between the movable and the fixed mold carrier alwaysextend out of one of them so that special and very expensive measuresmust be taken to guarantee the free motion of the movable part and alsocoupling without interference.

There has also been proposed a force-closing, rather than aform-closing, locking action ofa movable part to a fixed part. However,purely force-closing locking systems have the disadvantage that thetransmittable force is limited by the coefficient of static frictionalone, so that, in connection therewith, a locking force more than twiceas great as the tension acting thereupon must be expended, and that thedanger of an accident, in case of failure of an element used to producethe static friction, is extreme.

SUMMARY OF THE INVENTION This invention relates to closing, locking andprestressing devices for casting molds and, more particularly, to such adevice assuring maximum operating speed and operating safety with aminimum of equipment expense, and maintaining an optimum balance offorces while overcoming disadvantages encountered heretofore.

The invention device is particularly designed for casting molds,particularly for injection and pressure molding, of the type having afixed mold part carrier, a supporting part with a shifting deviceattached thereto, at least two guides extending from the fixed mold partcarrier to the supporting part, with a movable mold part carrier movablealong the guides by means of the shifting device and anchorable to theguides, and with a hydraulic prestressing device acting upon the moldpart carriers through the guides, for pressing the mold parts together.

In accordance with the invention, two guide bars extend parallel to theshifting device and through the supporting part in guided relationtherein, and are connected to the movable mold part carrier. At leastone stop plate, movable on the shifting device, is connected to the twoguide bars. On the shifting device, on opposite sides of the stop plate,there are two mechanical stops which are connectable to the stop plate.Each of the guide bars is provided, between the supporting part and themovable mold part carrier, with a piston supporting a movable cylinderenclosing the cylinder. Each of the cylinders is connected to an ejectorplate, and controlled hydraulic pressure can be admitted into cavitieson opposite sides of the piston inside the cylinder on each guide bar.

This expedient leads to a decisive reduction of the moved masses, clueto the multiple function of certain machine elements, to unhinderedmotions of the movable mold part carriers due to the long guide lengthsprovided therefor, and to quick motions of all closing, locking andprestressing operations due to the v e of hydraulic elements havingsmall pressure medium volumes.

In the area of the fixed mold part carrier, each guide may be connectedto a prestressing piston movable in a cylinder provided on the fixedmold part carrier and, therefore, to the supporting part connected tothe op posite ends of the guides. The two mechanical stops may bemovable along the shifting device in order to limit both the openingmotion and the closing motion. The mechanical stops may be nuts,adjustable on an external thread on the cylinder of the shifting deviceand which, in a very simple manner, make possible assuring agreementwith the locking elements relative to the guides. The nuts, usable asmechanical stops, may be in driving connection with a transmission foradjusting purposes.

Two mechanical stops may be fixed at opposite ends of the shiftingdevice and, between them, there may be two stop plates adjustable alongthe guide bars and connectable to the fixed stops. At least one of the,

prestressing pistons may be connected to the guides by means of athreaded connection, and present gear teeth as part of a transmissionbetween adriving element and the prestressing piston. This provides fora very simple pulling out of the respective guide to facilitate clampingin place the casting mold. The driving element, and a part of thetransmission connected thereto and in engagement with the prestressingpiston, may be designed in the form of an attachable unit.

An object of the invention is to provide an improved closing, lockingand prestressing device for casting molds, particularly for injectionand pressure molding.

Another object of the invention is to provide such a device whichassures maximum operating speed and operatingsafety with the minimum ofequipment expense.

A further object of the invention is to provide such a device whichmaintains the optimum balance of forces while overcoming disadvantagesencountered in prior art devices.

For an understanding of the principles of the invention, reference ismade to the following description ofa typical embodiment thereof asillustrated in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a plan view, partly in sections, of a closing, locking andprestressing device embodying the invention; and

FIG. 2 is a transverse sectional view taken along the line IIII ofFIG.1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2, thebase plate 1 has connected thereto a fixed mold part carrier 2 andsupports guide bars or rails 5 and 5' for a movable mold part carrier 4.Movable mold part carrier 4 is disposed between a supporting part 3, onbase 1, and which is remote from fixed mold part carrier 2. Guides 10,11, 12 and 13 are attached to supporting part 3 by respective pairs ofnuts such as l5, l6 and 15, 16'. A portion of each guide 10, 11, 12 and13, especially in the range of motion of movable mold part carrier 4, isdesigned witha thread such as 20, 21, which is preferably a square orAcme thread. i

The ends of the guides l0-13 remote from their ends anchored insupporting part 3 end in respective threaded bolts 23 through the mediumof which respective screw-on prestressing pistons 25 are connected toeach guide 1013.'In coaxial relation with the respective guides 10-13,and pointing away from the guides, each prestressing piston 25 supportsa return piston 26. A respective cylinder for each prestressing piston25 is provided on fixed mold part carrier 2 by means of a cylindricalbore directly in the mold part carrier. Each prestressing piston 25 hasoperatively associated therewith a respective return piston 26 in arespective return cylinder 31 in a hood 32, each hood being connected tofixed mold part carrier 2 and enclosing a free space 33 for the axialmotion of the associated prestressing piston 25.

In movable mold part carrier 4, there are anchored, by appropriate,threaded pins 35, at least two guide bars 40 and 41 which extendbackwards through guide bores 44 in supporting part 3. The left ends ofguide bars 40 and 41 are provided with threaded stubs 47 which receivenuts 46 anchoring a stop plate 50.

Between movable mold part carrier 4 and supporting part 3, each guidebar 40, 41 is formed with a threaded section for the accommodation oftwo nuts53 and 54, which connect a shifting yoke 55 with the guide bars40, 41. Between threaded sections 51 of the respective guide bars andthe respective threaded pins 35 threaded into movable mold part carrier4, there are formed appropriate cylindrical sections 58, 59 eachhaving acylindrical or annular portion 60 serving as a piston. Each cylindricalsection 58, 59 supports a respective ejector cylinder 61, 62 receivingthe respective piston 60, and an ejector plate 64 is connected toejector cylinder 61, 62.

Supporting part 3 supports a shifting device 69 comprising a cylinder70, a piston 71 movable in cylinder 70 and a piston rod 72 connected topiston 71 and extending into the area between upporting part 3 andmovable mold part carrier 4, the cylinder 70 having an external thread73. Shifting yoke 55 is connected to the free end of piston rod 72 by anut 75 on a threaded supporting pin 74.

The external thread 73 on cylinder 70 of shifting device 69 is engagedby two stop nuts 76 and 77 having respective external teeth 78 and 79each correlated with a respective positioning device 80 and 81. Eachpositioning device 80, 81, having a respective housing 85, is movablealong supporting rods 82, 83 and has a pinion 88 which can be rotated bya hand wheel 86 through a shaft 87. Each pinion 88 is in drivingconnection with the external teeth 78, 79 of the respective stop nut 76,77.

In the area of guides 10-13, two shifting guides 91, 92, connected tomovable mold part carrier 4, support two halves 94, and 94', 95',respectively, of respective splitnuts 96, 96', whose threads are formedfor cooperation with the threads 20, 21 on guides 10-13. To open andclose any two split nuts 96, 96', there is provided, for each pair ofsplit nuts, a respective double cylinder 100, 100' with two pistons (notshown) movable therein, and respective piston rods 101, 102 eachconnected to an associated piston. The half 95 of strip nut 96 isconnected to piston rod 101, and a connecting rod 105 extends from half95 through half 94' of the other split nut 96, in the area of doublecylinder 100 and guide 11, to a rigid connection with half 95. On theother hand, piston rod 102 is in fixed connection with half 94 of splitnut 96 and, through a connecting rod 104, with the half 94 of split nut96. A corresponding locking arrangement associated with double cylinder100 is correlated with guides 12 and 13. The double cylinders 100, 100'are mounted on movable mold part carrier 4. Each of the guides 10-13carries a key guided in a corresponding keyway in fixed mold partcarrier 2.

A respective pinion is mounted in each hood 32, and its teeth cooperatewith external teeth 111 on prestressing pinion 25. Externally of hood32, a respective shaft 112, required for mounting each pinion 110, isprovided with a hex for the accommodation of a hand or motorized tool torotate the associated pinion 110.

The plastifier and injection unit needs no detailed description becauseit does not form a direct part of the invention. It may be moved, in aknown manner, relative to fixed mold part carrier 2 in order to bebrought into close contact with the sprue in a divisible casting moldwhich is partly attached to carrier 2 and partly attached to carrier 4.

The most essential control elements comprise a general machine control121 to which are connected the control coils 126 and 127, 131 and 132,136 and 137, and 141 and 142 of the respective valves 125, 130, 133 and140. A pump 123 pumps hydraulic pressure medium from a tank or reservoir122 into a pressure line 124. interposed between pressure line 124 andvalves 125, 130, 135 and 140 there are respective correlated controldevices 128, 133, 138 and 143.

A mold closing stroke line 155 extends from valve 125 to the left end ofcylinder 70, and a return stroke line 156 extends between valve 125 andthe right hand end of cylinder 70. An ejector line 160 extends fromvalve 130 to the cylindrical sections 58, 59 and through these into thefront cylinder cavities 66 of ejection cylinders 61, 62. A return line161 extends from valve 130 to cylindrical sections 58, 59 and throughthese into the rear cylinder cavities 67 of ejection cylinders 61, 62. Anut locking line 165 extends from valve 135 to the two double cylinders100, 100', into their central regions, and a nut on locking line 166extends from the outer ends of double cylinders 100, 100' to valve 135.A prestressing line 170 extends from reversing valve 140 into thecylinder bores 30 of all the prestressing pistons 25 on the guides -13in fixed mold part carrier 2, and a return line 171 extends from all thereturn cylinders 31, in hoods 32, to valve 140.-

Closing, locking and prestressing devices for casting molds areessentially operated purely hydraulically. At the start of setting up,valve 130 is reversed so that pressure medium is supplied into thecylinder bore 67 of ejection cylinder 61, 62, moving these cylindersaway from movable mold part carrier 4 to bring ejector plate 64 into itsrear or rest position. After the parts of the casting mold formed withthe mold cavities are attached to the respective mold part carriers 2and 4, and after valve 125 is reversed, pressure medium is supplied bypump 123, in the quantity prescribed by control device 128, to closingstroke line 155 into cylinder 70 of shifting device 69. Piston 71 incylinder 70 is moved in the direction of its fastening to moldsupporting part 3. Through piston rod 72, shifting yoke 55 andcylindrical sections 58, 59 of guide bars 40 and 41, movable mold partcarrier 4 is moved toward fixed mold part carrier 2 until the two halvesof the casting mold rest against each other.

When setting up the machine, for example when the casting mold is closedfor the first time, this closing motion proceeds slowly and with littlepressure in the hydraulic system, especially in closing stroke line 155.By reversing valve 135, pressures medium is supplied through nut lockingline 165 between the two pistons in each double cylinder 100, 100, sothat the latter move the respective piston rods 101, 102 and thus,through connecting rods 104, 105, the correlated halves 94 and 95 ofnuts 96 and 96 which are assigned to the guides 10, 11 and, similarly,to the guides 12, 13. This determines the possibility of cooperation ofthe split nuts with threads 20, 21 on guides 10, 11, 12 and 13. If thisis not possible immediately, the movable mold part car rier 4 is movedback until the split nuts 96, 96' close completely on all of the guides10-13. In this position, positioning device 81 is adjusted so that itsstop nut 77 41. Positioning device 80, with stop nut 86, is positionedto the required return stroke up to the desired opening distance betweenthe halves of the casting mold. These positions of stop nuts 76 and 77along thread 72 on cylinder determine the end positions of the closing,locking and prestressing device during its operation.

Subsequently, the operating pressures oon the pressure medium suppliedto valves 125, 130, and

aredetermined by the respective control devices 128,

133, 138 and 143. Valve 140 is reversed, and high pressure medium issupplied through prestressing line 170 into the bores of cylinders 30for action upon all of the prestressing pistons 25 correlated withguides 10, 11, 12 and 13. The axial motions of pistons 25 in theirassociated cylinder bores 30 move the associated guides 10-13 and thesupport part 3 connected thereto, as well as, through split nuts 96, 96on movable mold part carrier 4, the mold half fastened thereto, againstthe half of the casting mold on fixed mold part carrier 2. The castingmold closes and is charged with the desired or prescribed prestressingforce. Plastifier and injection unit 120 is placed against the sprue ofthe casting mold, and the casting operation, such as the injection ofmolten or liquid material, can take place.

After the required time for cooling the cast melt, valve 140 is switchedback into the illustrated position. Pressure medium drains from cylinderbores 30, and prestressing pistons 25, under the influence of theelastic relaxation of guides 10-13, are again moved axially intocylinder bores 30, which corresponds to a motion of support part 3 andof movable mold part carrier 4 away from fixed mold part carrier 2. Thismotion of the prestressing pistons, together with the guides 10-13, issupported by the supply of pressure medium from return line 171 intoreturn cylinders 31 in hoods 32, to appropriately charge return pistons26 associated with prestressing pistons 25.

After the conclusion of this relief and return motion, which ismonitored by limit switches which have not been shown, pressure mediumis pumped throcgh nut loosening line 166 into the cavities of doublecylinders 100, 100 on the sides toward their piston rods. At the sametime, through reversed valve 135, pressure medium flows through nutlocking line into tank 122. This causes all of the split nuts 96 and 96,correlated with the guides 10-13, to be retracted from their intimatecontact with the threads 20, 21 on the guides through piston rods 101,102 and the associated connecting rods 104, 105. At the end of thisreturn stroke, again monitored by limit switches, valve 125 is returnedinto the illustrated position by appropriately energizing controlwindings 126, 127. Pressure medium is pumped through return stroke line156 into the cavity of cylinder 70 on the piston rod side, and isapplied to piston 71. Piston 71 moves within cylinder 70 from itsposition in the area of stop nut 77 toward the near stop nut 76 onexternal thread 73 of cylinder 70. This causes movable mold part carrier4 to move away from fixed mold part carrier 2, due to the pin 74 onpiston rod 72 carrying the nut 75 secured to shifting yoke 55 to whichguide bars 40 and 41 are attached, particularly at their cylindricalsections 58 and 59. This motion is terminated by stop nut 76, againstwhich there engages stop plate 50 on guide bars 40, 41.

During or after the motion of movable mold part carrier 4 away fromfixed mold part carrier 2, valve 130 is reversed one or several timesthrough the correlated control windings 131, 132 so that, due to suchreversing pressure medium flow in cylinder bores 66, 67 of ejectioncylinder 61, 62, these ejection cylinders and the ejectorplate 64, withthe ejectors connected thereto and extending into the casting mold, arereciprocated relative to the retracting or retracted movable mold partcarrier 4. These motions are generally terminated in a rear position ofejector cylinders 61 62 and ejector plate 64.

Often, casting molds too big to be placed on the two mold part carriersthrough the openings between the guides are used in injection andpressure molding machines. Pull-out guides are provided for such cases,and an example therefor is illustrated with respect to guide 1 1.

Movable mold part carrier 4 initially is moved as far as possible towardfixed mold part carrier 2 and, by means of split nuts 96 and 96', lockedto guides -13. A screwing tool is placed on the hex end 112 of pinion110 mounted in hood 132 and cooperating with the external teeth 111 onthe prestressing piston 25. The screwing tool may be a hydraulic motor,a wrench, a

ratchet, or the like. Turning the pinion 110 also causes theprestressing pinion 25 to turn, so that it will be removed from thethreaded bolt 23. After the complete removal of prestressing piston 25,loosening of nuts and 16' on guide 11 in the area of supporting part 3,and loosening of split nuts 96, 96', the preparations for pulling guide1 1 out are complete.

This guide 11 can now be clamped, by a suitable clamping device,relative to movable mold part carrier 4 so as to be immovable. Bycharging piston 71 through return stroke line 156, movable mold partcarrier 4 and, with this element, guide 11 clamped to it are moved outof the range of fixed mold part carrier 2 so that space is freedlaterally to manuever a bulking cast ing mold between the bars. Toassure unmistakeable conditions in the operation of the closing, lockingand prestressing device for casting molds, a keyway is provided in fixedmold part carrier 2 and the key 18 cooperating with the former in guide11 for the reassembly of guide 11 with prestressing piston 25.

The closing, locking and prestressing device for casting molds,embodying the invention, permits, in a surprising simple manner, purelyhydraulic operation with exclusively linear motions, and also reliablyform-closing locking before the build-up of the large locking forces,high motional accuracy due to very long guide lengths with the movablemold part carrier along the guide bars through the supporting part up tothe stop plate in the area of the shifting device, and importantsimplifications of the ejector mechanism. In addition, the distancestraversed by the movable mold part carrier, for closing and opening thecasting mold, are adjustable so as to be accurately reproducible, due tomechanical stops in the form of the stop nuts on the shifting device andin cooperation with the stop plate.

Varying from the illustrated design, but representing a self-suggestingmodification, there may be provided, at both ends of shifting device 69,particularly cylinder 70, fixed stop plates and two adjustable stopsalong guide bars 40, 41 for the limitation of the closing and openingmotions.

In place of attachable tools, appropriately controlled fixed motors alsomay be associated with pinions to turn these pinions. Instead of threadson the guides 10-13, a longitudinal succession of annular grooves closedin themselves may be formed on these guides, and be correlated withcooperating sleeves on the movable mold part carrier instead of thesplit nuts. In this connection, it is of advantage, in certain cases,when this succession of grooves on the guides is essentially of sawtoothdesign, in cross-sectional view, as this design is particularlyfavorable from a strength point of view.

While a specific embodiment of the invention has been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:

1. In a closing, locking and prestressing device for casting molds,particularly for injection and pressure molding, of the type havingafixed mold part carrier, a supporting part having a shifting deviceattached thereto, at least two guides extending from the fixed carrierto the supporting part, a mold part carrier movable by the shiftingdevice along the guides and anchorable thereon, and a hydraulicprestressing device acting through the guides upon the two mold partcarriers, the improvement comprising, in combination, relativelyelongated guide means extending parallel to said shifting device throughsaid supporting part in guided relation therein and connected to saidmovable mold part carrier; at least one stop plate movable along saidshifting device and connected with said guide means; mechanical stopsprovided on opposite sides of said stop plate and engageable therewith;said guide means being provided, between said supporting part and saidmovable mold part carrier, with piston means supporting movable cylindermeans enclosing said piston means; an ejector plate connected to saidcylinder means; and cavities in said cylinder mea s on opposite sides ofsaid piston means and cont ollably chargeable hydraulically.

2. In a closing, locking and prestressing device, the improvementclaimed in claim 1, in which said guide means comprises two relativelyelongated guide bars; said piston means comprising a respective pistonon each guide bar and said cylinder means comprising a respectivecylinder on each guide bar and closing the associated piston.

3. In a closing, locking and prestressing device, the improvementclaimed in claim 2, in which each of said guides, on that part of saidfixed mold part carrier facing away from the casting mold, carries arespective prestressing piston; respective cylinders on said fixed moldpart carrier each receiving a respective prestressing pinion; saidsupport part being movable; and means connecting the opposite ends ofsaid guides to said support part.

4. In a closing, locking and prestressing device, the improvementclaimed in claim 2, in which said two mechanical stops are movable alongsaid shifting device.

5. In a closing, locking and prestressing device, the improvementclaimed in claim 4, in which said shifting device comprises anexternally threaded cylinder; said mechnical stops comprising nutsthreadedly adjustable along said externally threaded cylinder.

6. In a closing, locking and prestressing device, the

improvement claimed in claim 3, in which at least one of said guides isformed with a threaded bolt portion threadedly engaged with theassociated prestressing piston; said associated prestressing pistonbeing formed with teeth forming part of the transmission between theassociated prestressing piston and a driving element for rotating saidassociated prestressing piston.

9. In a closing, locking and prestressing device, the improvementclaimed in claim 8, in which said driving element and a part of thetransmission in engagement with said associated prestressing piston isdesigned in the form of a unit attachable to the other transmission partof any of said prestressing pistons.

1. In a closing, locking and prestressing device for casting molds,particularly for injection and pressure molding, of the type havingafixed mold part carrier, a supporting part having a shifting deviceattached thereto, at least two guides extending from the fixed carrierto the supporting part, a mold part carrier movable by the shiftingdevice along the guides and anchorable thereon, and a hydraulicprestressing device acting through the guides upon the two mold partcarriers, the improvement comprising, in combination, relativelyelongated guide means extending parallel to said shifting device throughsaid supporting part in guided relation therein and connected to saidmovable mold part carrier; at least one stop plate movable along saidshifting device and connected with said guide means; mechanical stopsprovided on opposite sides of said stop plate and engageable therewith;said guide means being provided, between said supporting part and saidmovable mold part carrier, with piston means supporting movable cylindermeans enclosing said piston means; an ejector plate connected to saidcylinder means; and cavities in said cylinder means on opposite sides ofsaid piston means and controllably chargeable hydraulically.
 2. In aclosing, locking and prestressing device, the improvement claimed inclaim 1, in which said guide means comprises two relatively elongatedguide bars; said piston means comprising a respective piston on eachguide bar and said cylinder means comprising a respective cylinder oneach guide bar and closing the associated piston.
 3. In a closing,locking and prestressing device, the improvement claimed in claim 2, inwhich each of said guides, on that part of said fixed mold part carrierfacing away from the casting mold, carries a respective prestressingpiston; respective cyliNders on said fixed mold part carrier eachreceiving a respective prestressing pinion; said support part beingmovable; and means connecting the opposite ends of said guides to saidsupport part.
 4. In a closing, locking and prestressing device, theimprovement claimed in claim 2, in which said two mechanical stops aremovable along said shifting device.
 5. In a closing, locking andprestressing device, the improvement claimed in claim 4, in which saidshifting device comprises an externally threaded cylinder; saidmechnical stops comprising nuts threadedly adjustable along saidexternally threaded cylinder.
 6. In a closing, locking and prestressingdevice, the improvement claimed in claim 5, in which said nuts haveexternal threads; and correlated drive mechanisms in driving connectionwith said nuts through said external threads for adjusting said nutsalong said externally threaded cylinder.
 7. In a closing, locking andprestressing device, the improvement claimed in claim 2, in which saidtwo mechanical stops are fixedly connected to said shifting deviceadjacent the opposite ends thereof; and two stop plates movable alongsaid guide bars between said two mechanical stops and securable thereto.8. In a closing, locking and prestressing device, the improvementclaimed in claim 3, in which at least one of said guides is formed witha threaded bolt portion threadedly engaged with the associatedprestressing piston; said associated prestressing piston being formedwith teeth forming part of the transmission between the associatedprestressing piston and a driving element for rotating said associatedprestressing piston.
 9. In a closing, locking and prestressing device,the improvement claimed in claim 8, in which said driving element and apart of the transmission in engagement with said associated prestressingpiston is designed in the form of a unit attachable to the othertransmission part of any of said prestressing pistons.